Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$106.92	9.592%	$117.1758	$117.18	$117.20	$117.20
Purchase #2	$238.50	10.640%	$263.8764	$263.88	$263.90	$263.90
Purchase #3	$196.73	7.631%	$211.7425	$211.74	$211.75	$211.70
Purchase #4	$80.92	12.216%	$90.8052	$90.81	$90.80	$90.80
Purchase #5	$178.39	10.161%	$196.5162	$196.52	$196.50	$196.50
Purchase #6	$71.62	7.749%	$77.1698	$77.17	$77.15	$77.20
Purchase #7	$119.48	13.211%	$135.2645	$135.26	$135.25	$135.30
7 purchase totals =	$992.56		$1,092.5504	$1,092.56	$1,092.55	$1,092.60